Rugged normalizer for sorting circuit



Aug. 20, 1957 D. c. cox

RUGGED NORMALIZER ,FOR SORTING CIRCUIT 5 Shee ts-Sheet 1 Original FiledDec} 15, 1948 INVENTOR. DA V/D C- COX 'Arrae/vn Aug. 20,1957 c, cox v2,803,754

RUGGED NORMALIZER FOR SORTING. CIRCUIT Original Filed Dec. 15, 1948 5Shee tsfSheet 2 a Q 0 f a JNVENTOR. o \9 .DA V/D C- CQX BY 0 "0 JAM,

., a, flwfl V D. C. COX

RUGGED NORMALIZER FOR SORTING CIRCUIT Aug. 2,0, 1957 5 Sheets-Sheet '3Original Filed Dec. 13 1948 OF TRIM [L [fig/4 INVENTOR. .DA 0 0 coxArk-019,110

Aug. 20, 1957 c, cox 2,803,754:

" RUGGED NORMALIZER FOR SORTING CIRCUIT Original Filed Dec 15, 1948 I 5Sheets-Sheet 4 25 23 79 8/ 8384- a: a 6i [h INVENTOR. DA v/o ccox falwix v ATTOE/VE) Aug. 20, 1957 D. c. cox 2,803,754

RUGGED NORMALIZER FOR SORTING CIRCUIT Original Filed Dec. 13, 1948 5Sheets-Sheet 5 INVENTOR .DA V/D C. C OX United States Patent z,se3,7s4RUGGED NORMALIZER non sonrmo cIricUiT David C. Cox, Grand Rapids, Michassignor to Mandrel Industries, Inc., a corporation of Michigan Originalapplication December 13, 1943, Serial Np. 64,967. Divided and thisapplication November 15, 1952, Serial No. 320,802 r 7 Claims. (Cl.250-414) This application is a division of my application, Serial Number64,967, filed December 13,- 1948, which is now U. S. Patent 2,656,923,granted October 27, 1953;

My invention relates to article sorting and to avoiding errors inoperation of sensitive electronic circuits responsive to characteristicsof articles being sorted.

and reliable sorting of articles which are sorted byeriiployment oftheir light reflective properties A further object is to normalize. orstabilize electronic circuits for rendering them unaifected byunavoidable changes in such circuit constants and electrical propertiesas tend to cause drift in the magnitude of input values which arerequired to produce circuit'actuati'on, An object of the invention is toprovide reliability in the assurance of maintenance of the samesetting'ove'r a long period of time in the optical sorting of articlesand to provide a rugged normalizer for use in amplifier circuitsespecially for photoelectric devices. H

A further object of the invention is tojenable articles such as lemonsand other fruits and relatively fragile articles to be sortedautomatically at a"high rate ofspeed without bruising or otherwisedamaging the articles.

Still another object of the invention is to enable amplifiers of theelectronic type to operate in a manner'simulating characteristics oflong time constant circuits, so as to obtain very precise, sensitive,and accurate response or actuation as a result of minute deviation inthe light reflective properties of a sorted article from a predeterminedstandard of comparison, while retaining characteristics simulating thoseof short-time-constant circuits forenabling the circuit to be normalizedor haye its bias cor; rected very quickly during the intervals betweensorting operation, in order to compensate for circuit variations anddrift in characteristics of various circuit elements;

Other and further objects, features and advantages of the invention willbecome apparent as thedescription proceeds. In carrying out theinvention in accordance with a preferred form thereof, as applied to thesorting of articles such as lemons, I provide a framework supporting atthe upper portion thereof, a substantially horizontal conveyor adaptedto receive lemons or other articles atone end and having a sorting headmounted below the other end of the conveyor. The sorting head includes alamp housing having a vertical passageway therein for freely fallingobjects with an upper gate normally closing the upper end of thepassageway and a lower gate at the lower endof the passage for enablingthe objects to be diverted in one direction or another, accordingto theresponse produced in the sorting mechanism. The lamp housing has sidewalls shaped to form a hexagonal prism and lamps mounted slightly beyondthe upper and lower edges of the side walls for indirectly illuminatingthe interior of the-lamp housing and casting diffused light upon thearticles falling along the axis of the prism. Background screens 01''reference backgrounds are provided along three alternate t is an objectof the invention to obtain moreaecurate 2,803,754 Patented Aug. 20, 1957vertical walls of the prism to serve as standards of comparison of thelight reflective properties of the articles being sorted, and at thethree remaining side walls lightreceiving and directing elements areprovided.

If desired, each of these light-receiving and directing elements maycomprise a lens system adapted to form receivedlight into a beamprojected against a photoelectric tube. Preferably, however, two of thelight-directing elements comprise mirrors mounted at such an angle as toreflect the lighttoward the Wall containing the lens system forming theremaining light-directing element, and a single photoelectric tube isprovided for response to the reflected light in all three of the beamsof light. This arrangement is preferable for the sake of simplicity andminimum cost of apparatus, especially in the case of a photoelectricsorting operation carried out by what is known as the light trip method.This is a method in which the mechanism is actuated whenever the lightrefiective properties of the article integrated over substantially theentire surface thereof exceed a predetermined value. In other words thelight trip method is the one in which all lemons lighter than apredetermined standard produce actuation of the mechanism, tripping thelower gate open and enabling such lemons to fall into one receptacle,and all lemons darker than the predetermined standard produce noactuation of the inech'anisiri in consequence of which the lower gatediverts su'ch lemons into another receptacle. t 1 Preferably electronicamplifiers are emp leye tor in} c're'asing energy output of thephotoelectric tube suiiic'iently to cause operation of an electro-magnetplunger or the like for tripping the lower gate. I

Cam mechanism or the equivalent is preferably provided for opening andclosing the upper gate at apredetermined rate and a second cam mechanismor eccentric, or equivalent mechanisrn, is provided for resetting thelower gate to the closed or diverting position at the same rate.Mecha'nical drive is provided with gearing of such ratio and so relatedto the cam and the eccentric thatan article progresses to the end of theconveyor and falls upon the upper gate once for each operation of theupper gate, and during the time interval while the upper gateis closedaf ter it has allowed the previous article to fallthrough the pas sagein the lamp housing. Likewise, the connections are s'tich as to causethe eccentric to reset the lower gate once for each operation of theupper gate during the interval after an article has fallen through thepassage ina lamp housing and while the upper gate is closed.

Although the invention is not limited thereto, preferablyd employ athyrat-ron type of tube, that is a vapor 'discharge or gaseous dischargeamplifier tube, forenergizing the tripping magnet of the lower gatewhich causes it to open upon actuation of the lighbresponsive mechanism;One or more stages of vacuum tube amplification are interposed betweenthe photoelectric tube and the control electrode or grid of thethyratron tube. A circui-tjbreaking switch or commutator alsosynchronized with flre conveyor, upper gate cam, and the lower gateresetting mechanism is provided in the anode supply circuit of thethyratron tube in order that it may be deenergized after each operationof the lower gate tripping mechanismand be prepared for a subsequentoperation.

Directacurrent amplifiers may be made very sensitive,- and so long asthey remain in exact calibration give very precise results in measuringor detecting quantities in terms of a predetermined standard. However,they are subjectto drift and any variations in 'the bias potentialintroduce substantial errors. Moreover, tube aging progressively variesthe relationship between signalinp'ut 0 and-output. 'Sincedirect-current amylifiers are ordinar I ily characterized by a direct orconductive connectionbe-i.

tween the input signal terminals or the preceding stage and the grid,the requisite bias voltage source must be included in the grid signalcircuit, usually in the form of a C battery, which itself is a largesource of error since such C batteries are subject to change in voltage.

On the other hand, alternating current amplifiers, characterized :bynon-conductive coupling such as condenser coupling between stages orbetween the input signal terminals and the grid circuits remain incalibration relatively well because they reset their bias continually.They respond to the change in magnitude of the signal rather than itsabsolute value so that retention of a precise bias is relativelyunimportant. However, alternating-current amplifiers are generally lesssensitive than direct-current amplifiers, and they are responsive to therate of change of signal magnitude, that is the speed with which thechange in the potential takes place. Therefore the response depends uponthe speed with which the signal is applied and removed, which is nottrue within reasonable limits of direct-current amplifiers. The maxi-mumall-wable speed of sorting, that is the frequency of presenting signalsto the alternating amplifier, depends upon its timeconst-ant. If severallarge signals have previously been received in rapid succession thealternating-current amplifier tends to adopt such previous signals asthe reference point instead of the fixed bias or a standard comparisonsignal if a reference background is used. From one standpoint a shorttime constant is desirable in order to permit restoring the circuit tostandard conditions rapidly between signals; that is, to minimize theeffect of previous signals; but from another standpoint a long timeconstant is desirable in order that the circuit will hold itscalibration while the present signal is being amplified so as to providehigh accuracy of sorting.

Accordingly, what is desired is an amplifier having both the speed andsensitivity of a direct-current amplifier and the ruggedness andrelative independence of bias settings of an A.-C. amplifier togetherwith further provisions for insuring stability and accuracy.

In accordance with my invention I achieve the desired results by, ineffect, connecting the circuit as a long-time constantalternating-current amplifier free from loading effects when a signal isreceived from an article to be sorted and as a very rigidly controlleddirect amplifier when a standard reference signal is applied forcomparison. The arrangement for this purpose I call a normal.-

In order that the point at which the thyratron is tripped in relation tothe intensity of the illumination of the photoelectric tube will remainaccurately constant and unaffected by various tendencies toward drift,such as aging of the various tubes and filaments, heating of resistors,variations in filament voltage, dust, fingerprints and the like in thelens system and other portions of the optical system, the mechanism isprovided with whatl call a normalizer. The normalizer serves forintermittently resetting the bias of the lower gate operating tube ortripping at which it is neutral with respect to the photoelectric tube.This is accomplished by providing a condenser coupling between the anodeof the vacuum tube amplifier and the control grid of the thyratron, orbetween two equivalent points of the circuit, and resetting thepotential on this condenser intermittently and preferably subsequent toeach operating cycle of the light trip mechanism.

For the sake of obtaining high precision the condenser is preferablyrelatively large and for the sake of obtaining high gain the vacuum tubeload resistor or anode resistor is preferably relatively large and thevacuum tube is preferably -a pent-ode tube. Normalization isaccomplished by intermittently connecting one side of the norm'alizingcondenser to a point maintained at a predeter mined potential. The useof such large condensers and large load resistors, however, tends toresult in a very long time constant preventing complete normalization ofthe condenser potential difference during the brief interval of timeallowed in the short operating cycle corre sponding to a high sortingspeed and high frequency of presentation of articles to thephotoelectric system. in order to obtain the equivalent of a short-timeconstant during the normalizing operation, one or more cathode followertubes are employed. At least one cathode follower tube is employed whichis interposed bet-ween the last stage vacuum amplifier anode and thethyratron control grid so that the charging or discharging current ofthe condenser during normalization is provided through the cathodefollower instead of an anode resistor or other circuit constants. Inorder to enable a potential-supply of low-current output to be employedfor normalizing, a second cathode follower is preferably also provided.

In accordance with my invention, during normalization or resetting ofthe circuit against the comparison signal or background, the circuit isconnected as a short-time constant direct-current amplifier and duringexamination of the article to be sorted, the circuit is connected as along-time constant alternating-current amplifier and it is unnecessaryto utilize electrical circuit elements in which the electrical Valuesare compromised between the conflicting requirements during the periodwhen the article is being examined and during the interval betweenexamination of articles when it is desired that a circuit should restoreitself to a standard setting.

A better understanding of the invention will be afforded by thefollowing detailed description considered in conjunction with theaccompanying drawings, in which: 7

:Fig. 1 is :a side elevation partially in section of a photoelectriclemon sorter forming an embodiment of the invention;

Fig. 2 is a fragmentary end view of the apparatus of Fig. 1 as seen fromthe left-hand end;

Fig. 3 is a perspective view of the portion of the apparatus of Fig. 1including the lamp housing;

Fig. 4 is a CIO'SSaSQCllODLl view of the lens housing represented as cutby a horizontal plane 44 indicated in Fig. 1; l

Fig. 5 is a vertical mid-section of the portion of t s apparatus shownin Fig. 4;

Fig. 6 is a perspective view of the lamp housing employed in theapparatus of Fig. 1;

Fig. 7 is .a plan view of the apparatus of Fig. 1;

'Fig. 8 is an end elevation partially in cross-section of the apparatusof Fig. 1 as seen from the right-hand end;

Fig. 8A is a fragmentary view of a portion of the apparatus of Fig. 8,showing the lower gate resetting mechanism in another position;

Fig. 9 is a developed view of a drum switch used in the apparatus ofFig. 1;

Fig. 10 is an enlarged, detail plan view of the upper gate of theapparatus shown in Figs. 1 and 7;

Fig. 11 is a fragmentary view partially in section of the apparatus ofFig. 10 represented as cut by a vertical plane 1111;

Fig. 12 is a schematic and circuit diagram of an alternative form ofelectrical mechanism which may be employed in the apparatus of Figs. 1to 11;

Fig. 13 is a schematic and circuit diagram of the apparatus of Figs. 1to 11 employing an optical system such as illustrated in Figs. 3 and 4;

Fig. 14 is a fragmentary view of the upper-gate operat ing mechanism;and

Fig. 15 is a plan view of the lower gate.

Like reference characters are utilized throughout the drawings todesignate like parts.

The apparatus shown by way of illustration in Fig. 1 comprises asuitable framework 11 supporting a conveyor system 12, shown as being ofthe screw type with a drive motor and speed-reduction gear unit 13,gearing 14, a timer shaft 15 with associated apparatus to be describedin greater detail hereinafter, a lamp housing and viewing chamber 16, alens housing 17, a photo-electric tube housing 18, an amplifier case 19and lemon receptacles 20- and 21,- only one of which-is visible in 'Fig,1.,

As shown more clearly in Fig. 7, the lemon conveyor 12 comprises a pairof horizontal shafts 23 and 24 set close enough together so that thelemons or other articles to be sorted cannot fall through thespacebetween them. One of the shafts 23 has a helical flange or screw 25,formed by a length of large copper tubing wound upon the shaft andsecured thereto. Ordinarily the initial pitch of the helix 25 is sochosen as to exceed the maximum expected dimensions of the articles tobe sorted, such as lemons, so that the articles will be spaced, as shownin Fig. 7, at distances of the order once-and-a-half or twice theirmaximum dimensions. Preferably the spiral 25is graduated so that itspitch increases along the length of travel for causing the separationbetween articles to increase. The space behind the spiral may be filledin to form a spiral groove of .substantially constant width. Theconveyor shafts 23 and 24 extend from the left-hand end 26 at which thearticles to be sorted are deposited thereon to a point above an uppergate 27 pro vided above the lamp housing 16.

The drive mechanism 14, as illustrated in Figs. 2 and 7 for the conveyor12, comprises a jack shaft 28- carrying a drive pulley 29 and a gear 31with which. are meshed two driven gears or pinions 32 and 33. Thepinions 32 and 33-are keyed to the conveyor shafts 23 and 24 re-.spectively. There is a belt or chain 34 enabling the pulley 29 to bedriven by the motor 13, which may in-. clude speed-reduction gearing,not separately shown. The timer shaft 15also carries. a pulley 35 overwhich the belt .or chain. 34 passes The relative diameters. of thepulleys 29 and35 in relationstothe relative diameters of the gear31andthepinions32 and .33 areso chosen that the timer shaft 15 rotatessynchronously with the conveyorishaft 23,. assuming a single pitch screw25. It is to be..understood that the arrangement ofthe mech-. anismdriven by the timer shaft 15 and the conveyor 12 issuch. that one.operation of the mechanism .driven by thetimershaftlS is obtainedforeach delivery. ofan.

article, suchas a lemon 36, from the conveyor 12 .to the upper gate.27.

The lamp housing 16 preferably comprisesside walls, illustrated. in Fig.6, formed in the shape of a hexagonal prism. For example, sheet metalmay be bent to shape, as shown, with one or more joints 37 welded orbrazed to form a unitary structure. Each of the side walls or faces..38is providedwith an opening 39 to receive an. opticaldevice, such as abackground screen or. a lightdirjecting object such as a mirror or .lenssystem, as will be described more in detail hereinafter. Annular lamppockets or channels 41 and 42 arejoined to thehexage onally formed. sidewalls 38 at their upper and lower edges respectively. The upper wall 43of the upperlamp channel 41 is extended inwardly toform the top wall forthe lamp housing16 with an opening 44 therein at which the upper gate,27is mounted. Likewise, the lower wall 45 of. the.lower lamp channel 42 isextended inwardly to form a lower, wall for the lamp housing 16 with anopening therein. Lamps 47 are mounted in the lamp channels .41 and 42.In order to shield the falling lemon 36rfr-orn .thedirect rays of lightfrom any of the lamps 47, flanges.50 areprovided, as shown in thedrawing. There are shields 4S and :49 joined respectively to theupperwall 43 .at the edge of the opening 44 and to the lower wall 45atthe. edge of. the opening 46, for equalizing the illumination of thearticle 36 from various directions, by overcoming excessive light fromthe ceiling and the floor of the lamp housing.

In the hexagonal lamp housing good side lighting is proyided owing ,tothe indirect light on the six walls Moreover, any tendency of the topand bottom members of the lamp housing to get excessive light owing totheir being directlylighted by lamps quite close to these mem bersand tolightthe tops and bottoms of lemons excessively is avoided by theconstruction provided and illustrated; The entrance and exit hexagonalcolumns are lined with black and appear as dark zones. They havefurthermore been introduced in the lamp housing just farenough asillustrated,.so that their shadowaccurately neutralizes the excesslightfronn the top and bottom light ringsl The lens housing 17 is setinto one of the side wall openings 39 so as to close the same. As willbe explained in the course of further description, the other openingsare also closed so that the lamp housing 16 forms a light-tight box,except for the upper opening 44 and the lower opening 46, between whicha vertical pas sageway is formed for objects 36 falling from the end ofthe conveyor12. The space in this passageway between the lower edge ofthe shield 48 and the upper edge of the shield 49 forms a viewingchamber in which all sides of the objects 36 are exposed to the view. ofa photoelectric cell in the cell box 18, without anynecessity forholding theobject an d without any portion of the object being obscuredby a lamp or by a holder, rest or other support. The upper opening 44 ofthe lamp housing 16 is normally substantially closed by the upper gate27: The lower opening 46 is not closed but relatively little lightenters the lamp housing 16 from below.

Instead of a lower closure at the lower end of the passageway 44 and 46,a resiliently constructed. lower gate. 51 is provided having a normalposition sloping, as shown in Fig 8, and adapted to be dropped to alower or fully opened position, as represented in Fig, 8A,in which thelower gate is substantially vertical. A cam or eccentric mechanism,driven by the timer shaft 15, as described more fully hereinafter, isprovided for operating the upper gatej27 and for resetting the lowergate 51.

The receptacles 20 and 21 which may take the form of bins or, in thecase of fragile articles, flumes containing flowing water for floatingthe sorted articles away, are

mounted on either side of the point directly below the lower opening 46.The receptacle 20 is so mounted that the articles falling upon the lowergate 51 in its normal position are diverted into the receptacle 20. Aresilient diversion chute 52is provided directly below the opening 46for diverting the falling articles into the receptacle 21 when theilowergate 51 hasbeen depressed to its fully opened position, illustratedin,Fig. 8A. Preferably the chute 52,is composed of a resilient material,such as rubber, plastic or thelike, to avoid damage to, the fallingarticles. i

The photoelectric mechanism may be made responsive either to the coloror the reflectivity ofthe article falling through the viewing chamberand the lamp housing 16. For thesakeof illustration, however, thephotoelectric mechanism will be described as being of the typeresponsive to reflectivity. It maybe set either for operation upon areflectivity exceeding a predetermined, value or for operationupon areflectivity falling below a prede terrnined value. For the sake ofillustration, it is assurned that it is set for what is known as lighttrip. In

this case the receptacle 20,is the receptacle for dark,

lemons and the receptacle 21 is the receptacle for light lemons. Thetimer shaft 15 and the mechanism driven by it are so set thatthe uppergate 27 opens asoften as the ,conveyor 12 deposits a lemon upon it, butslightly later than this instant. The timer mechanism is also soarranged as to reset the lower gate 51 to the position shown in Fig. 8,during the interval after an articlehas fallen through the lamp chamber16 and before the upper gate 27 is again opened. Accordingly, if thedemon 3.6 is lighter than a predetermined value for which the system isset, the lower gate 51 is depressed and the article is dropped into thelight lemon receptacle 21. On the other hand, if the lemon is darkerthan the predetermined value forwhich the apparatus is set, the gate 51remains in the position shown in Fig. 8 and deflectst'he article to thedark receptacle 20.

The photoelectric and amplifier apparatus for accomplishing theoperation of the lower gate 51, according to the light reflectivity ofthe falling article 36, is represented schematically by a circuitdiagram in Fig. 13.

As illustrated in Figs. 10 and 11, the upper gate 27 comprises aplurality of sector shaped doors or leaves 53 mounted upon hinges 54around the periphery of a circle coaxial with the lamp housing 16 at theedges of the hexagonalupper opening 44 of the lamp housing 16. To eachsector 53 is secured an operating lever 55, pro vided at the outer endwith a slot 56. For operating the levers 55 in unison, a ring 57 'isprovided which fits in each of the slots 56 and is adapted to be movedupward or downward according to whether the gate 27 is to be opened orclosed. For producing such vertical move ment of the ring 57, a pair ofarms 53 is provided, which are secured to a shaft 59 and connected tothe ring 57 by pintles 61. For'operating the arms 58 a crank 62 isprovided carrying a cam follower 63. A cam 64 adapted to. engage the camfollower 63, is mounted upon the timer shaft 15. It is to be understood,however, that the invention is not limited to the specific arrangementillustrated and equivalent mechanism may be provided for accomplishingopening and closing of the gate 27 synchronized with the operation ofthe conveyor 12. Preferably, a spring 65 is provided for holding the camfollower 63 against the edge of the cam 64.

In order to avoid damage to fragile articles, such as fruit, the lowergate 51 is composed of relatively resilient material, such as light,flexible, rubber-coated Wire rods for example, each secured at one endto a shaft 66, to which is secured an arm 67. In the arrangementillustrated, the arm 67 is provided with a spring 68 for depressing thegate 51 to the lower or fully opened position shown in Fig. 8A. There isa latch 69 for holding the arm 67 down and the gate 51 up against thetension of the spring 68. The latch, as illustrated schematically,comprises a sliding bolt 71 formed as an armature or plunger of asolenoidwinding 72, adapted to be energized by the amplifier 19 uponresponse to actuation of the photoelectric cell 18 for retracting theplunger 71 and tripping the gate 51.

For resetting the lower gate 51 and the latch 69 after each operation ofthe solenoid 72 a synchronously moving resetting rod 73 is provided. Therod 73 is suitably mounted for axially slidingmotion as in a guide 74and is arranged to be moved up and down in synchronism with theoperation of the upper gate 27, for example. As illustrated, aneccentric or crank arrangement may be provided comprising a crank disc75 mounted upon the timer shaft and a connecting rod 76 pivoted at oneend to the crank disc 75 by a pin 77 and at the other end to the upperend of the rod 73. The angular position of the crank pin 77 in relationto the dropping portion 78 of the cam 64 is such that the rod 73 ismoved downward for resetting the gate 51 slightly before the camfollower 63 is permitted to move to the right under the action of thespring 65 for opening the upper gate 27. In consequence, the gate 51 isin the reset position shown in Fig. 8, whenever the article 36 fallsthrough the vertical passageway of the light chamber 16. As shown in thedrawing the length of the rod 73 is such that its lower end bearsagainst the arm 67 and depresses it slightly below the catch 69 when thecrank pin 77 reaches its lowermost position.

The timer shaft 15 also carries a rotary switch or commutator includinga drum 79 cooperating with brushes 81, 82, 83 and 34. The drum 79, asillustrated in the surface development view of Fig. 9, comprises acylinder of insulating material 85 into which are set segments ofconducting material such as copper segments 86 and 87, having a shapeshown in Fig. 9. The arrangement is such that circuit interruptions takeplace between the brushes 83 and 84 and between the brushes 81 and 82once for each revolution of the shaft 15, but the circuit interruptionbetween the brushes 83 and 84 takes place while the circuit is closedbetween the contacts 81 and 82.

The lens housing 17, illustrated in Figs. 3 and 4, comprises apassageway165 for direct passage of the light beam intersecting the axis 103 ofthe lamp housing 16 to a photoelectric cell or tube 98, which includes alens system such as an objective lens 106 and a condensing lens 107. Asillustrated in the arrangement of Fig. 12, a photoelectric lens systemand a corresponding photoelectric tube may also be mounted in theopenings 88 and :39 of alternate hexagonally placed side walls in thelamp housing 16. Nevertheless, in the embodiment of Fig. 3 and Fig. 13,I have, in order to avoid the use of additional photoelectric tubes andin order to simplify the mechanism, employed mirrors 91 and 92 which aremounted upon suitable supports mounted on base plates for closing theopenings 88 and 89. The mirrors 91 and 92 are each mounted at such anangle that light beams, passing along horizontal lines intersecting thevertical axis 103 of the lamp housing 16 and impinging upon the mirrors91 and 92, are reflected along the axes of passageways 93 and 94 in thelens housing 17. The passageways 93 and 94 are also provided withsuitable lenses 95 for causing all three of the light beams to befocused at a common point within the casing 18 for the photoelectrictube 98. Preferably, transparent dust covers are provided. The remainingthree openings 96 in the side walls of the lamp housing 16 have mountedtherein removable background screens 97 or reference backgrounds of thetype described in my Patents No. 2,244,826, granted June 10, 1941(designated therein by the reference numeral 30), and No. 2,325,665,granted August 3, 1946 (designated therein by the reference numeral 46),to serve as standards of comparison of reflectivity of the articlesbeing sorted. Although the lamp housing has been described as ahexagonal prism, it will be understood that my invention is not limitedthereto, as a circular or curved surface side wall may also be employedwith the reference backgrounds and light-receiving and directing devicesmounted at approximately the same angles, viz. alternately, 60 degreesapart. In Fig. 4, the circle represents the clearance between light raysalong 93 and 94 and the directional errors of an article falling freelyalong 103 (as maximum envelope of paths).

The photoelectric amplifier, represented in Fig. 13, comprises, inaddition to the photoelectric tube 98, one or more sensitive amplifiertubes of the high vacuum type and a high current tube such as a gaseousor vapor discharge tube of the thyratron type for energizing thetripping coil 72. I have found, however, by reason of the improvedoperation obtained in accordance with my invention, that a single stageof amplification is ordinarily sufficient and I preferably employ asingle high vacuum tube 99 coupling the photoelectric tube 98 to athyratron tube 101. In order that a single stage of amplification may beemployed, a high vacuum tube 99 is preferably of the pentode type, c. g.a 6C6 type of tube may be employed, and for the sake of obtaining highamplification a high resistance load is provided for the tube 99consisting of an anode resistor 102 which may have a resistance of twomegohms, e. g. in the case of use of a 300 volt power supply.

For capacitatively coupling the thyratron 101 to the pentode 99 acondenser 103 is provided. The capacity of this condenser is maderelatively large. In addition, a bias-fixing connection for the grid ofthe thyratron 101 is, in effect, made through what amounts to infiniteresistance during the portion of an operating cycle that the apparatusis functioning for performing a sorting operation or selection. However,.in order that effective .bias of the thyratron 101 may be restored to afixed value and this may be done quickly after each operation, whatamounts to very low resistance bias connection is provided. This isaccomplished by the employment of a "normalizerf switch taking the formin thespecific apparatus illustrated of the brushes 83, 84 and the drumswitch segment 87. The capacity of the condenser 108 is made relativelylarge because the output terminal is connected to the grid of tube 111where minute grid currents will flow and, through a cable to one of thenormalizing brushes 83 where leakage currents may flow. Any suchcurrentscause displacement of. the setting and by the use. of large couplingcondensers the extent of the displacement is reduced to a negligiblequantity. In other words I aim to obtain, in effect, the characteristicsof a direct-current amplifier by approaching an alternatingcurrentamplifier with infinite time constant. Unavoidable leakage currentscause the actual appara tus to fall somewhat short of infinite timeconstant. However, by employing a condenser 108 having a capacity of twomicrofaradsinstead of .02 microfarad, e. g., the stability against leaksis improved by a factor of one hundred.

For the purpose of overcoming what would otherwise be the long timeconstant effect of the high pentode load resistance 102 and the highcapacity 108 in a circuit determining the accuracy and rapidity withwhich the potential of the grid of the thyratron 101 is restored to itspredetermined value after each operation of the apparatus, a cathodefollower 109 is interposed between the high potential plate of thecondenser 108 and the anode of the pentodetube 99. The rotary switchbrush 83 is connected to the low potential plate of the c011- denser 108and the brush 84 is connected to a suitable reference voltage which isselectedto bring the grid of the thyratron tothe desired proximity tothe tripping point and isthe effective voltage of the bias of thethyratron 101 determining the trip point of the thyratron 101 and thesolenoid coil 72. The reference voltage may be the actual criticalvoltage, any voltage above which would ignite the thyratron 101 whenapplied to its control grid. However, thyratrons are ordinarily operatedwith'relatively low trip voltage. It is more practicable to employ ahigher reference voltage of the order of 80 volts for example. The useof such a high reference voltage would necessitate a high cathode biasfor the thyratron. The thyratron may be so operated; but instead asecond cathode follower 111 is preferably interposed between thecoupling, condenser 108 and the control grid of the thyratron .101 for,in effect, translating the trip voltage to lower value.

A conventional voltage divider, consisting of resistors connected inseries across the regulated power supply may be employed as thereference voltage source. In order to. avoid the necessity forlow-resistance, highpower consumption resistors in the reference voltagesource to, assure substantialy instantaneous normalization, an,additional cathode follower 112 is interposed between the.rotaryswitchbrush 84 and a terminal 113 fromwhich the reference voltage isderived. It is to be understood that the invention is not limited to theuse ofcircuitelements with specific numerical values of electrical.constants.and specific values and tube types are given merely by way ofillustration. However, satisfactory results -have been obtained with thepentode 99 taking the formof a 6C6 tube, the thyratron 101 a 2050 tube,the cathode follower tubes 109 being the type 6SL7 tube. and the.cathode followers 111, 112 twin triode elements of a 631.7 type of tubewith a-300 volt power supply. The power supply is representedschematically at 114, but it is to be understood that conventionalrtypepower. pack, preferably regulated, is utilized in practice. Satisfactoryoperation of the cathode followers .109, 111 and 112 is obtained with20,000 ohm resistors connected to the grounded end of the power supply114. However, to avoid thenecessity for biasing the:cath0de ofthethyratron 101 positively, which ordinarily trips at approximately minusfour volts in the case of a 2050 tube, the cathode of the tube 111 is 10preferably connected to a point below ground potential. For thispurposeandinorder to simplify the circuit arrangement for obtaining light tripoperation, a negative power supply 115 isalso provided which may, forexample, be a 300 volt supply.

The cathode follower 111 is provided with cathode resistance consistingof resistors 116 and 117 .inseries, the additional resistance providedby'theresistor 117 being suflicient to provide additional voltage dropequaling the voltage of the, negative power supply 115. An inputconnection to the control grid of the. thyratron 101 may be taken from apoint on the resistor 117 whichmay be made adjustable by the use of asliding tap 118. The tap 118*is set at such a point that the normalpotential of the tap 118, with the grid of the cathode follower 111atthe reference voltage, is a suitable value, such as minussix volts forexample, in the case of a thyratron which trips at minus fourvolts.

The. cathode followers 109, 112 are also provided with cathoderesistances consisting respectively of resistors 119, 12.0'in series and121, 122 in series. The resistors 119, 121 may be connected directly tothe ground if desired, but, ifj the additional resistors 120, 122 areemployed, their values are so chosen as to give the same voltage dropasthe voltage of the negative source 115. The resistances of the cathoderesistors 119 and 121 represent, such as 20,000 ohms for example, theeffective load resistances of the cathode followers 109 and 112.

The reference voltage terminal 113 may be the junction terminal ofresistors 123 and 124, connected in series across thepower supply 114and having a suitable resistance ratio so as to give the desiredreference voltage, e. g. volts. In this case theresistors 116 and 117may be so.chosen as to cause thecathode of the cathode follower tube111to float at volts when the control grid is held at the potential 80volts, thereby rendering the voltage of the tap 119 highly sensitive torise in voltage of the control grid of the cathode follower 111 abovethe predetermined reference voltage, such as 80 volts.

From, the foregoing it will be apparent that the use of the normalizerswitch 79, withits contacts 83, 84 and 87 and thecathodefollower stagesbetween amplifier tubes, provides a very large. time constant when thearticle to be sortedis being examined by a photoelectric tube. At thistime, the switch i9is open andthe effective time constant corresponds tothat of insulation resistance and the large condenser. During .theinterval between such examinations the circuit is acting substantiallyas direct-current amplifier, with a directconnection between theamplifier grid and the bias potential, the connection providingsubstantially zero resistance and zero time constant.

Moreover, the use of the cathode follower tubefor supplying, the. biaspotential point insures a high degree of rigidity of the direct-currentamplifier characteristic since an unlimited'supply of current isavailable for obtaining the potentialswithout altering the potential ofthe voltage divided '123--124'by resistance drop. Thus there is noloading on the resistors 123-124 to produce errors in the bias voltage.The amplifier 99 is likewise free from loading errors by virtue of thecathode follower tube 109.

The pentode 99 is provided with suitable dropping resistors 125 and 126for providing the screen grid potential and preferably also with acathode resistor 127 for negativelybiasing the control grid, especiallywhen no negative powersupply is employed. A suitable grid resistor 128is provided as in conventional circuits.

The amplifier and normalizer circuit of Fig. 13 is described as used inconnection with a gravity sorting machine, such as a lemon sorter, whichI prefer to operate on a light trip for actuating a lower gate. It is tobe understood, however, that the photoelectric amplifier of Fig. 13isnot limited in use to the sorting machine herein described by way ofillustration and may be also used in numerous other types of.photoelectric sorting apparatus where either light or darp trip may bedesired and where 1 1 the output of the amplifier represented as thevoltage at the point 119 or at the point 83 may be further amplifiedbefore supplying it to a thyratron, or may be supplied directly orthrough amplification to sweep circuits of a cathode ray tube or inconnection with color sorting equipment and the like.

For enabling the circuit to operate with either light trip or dark trip,a triple-pole, double-throw switch 129 has been shown to illustrate thedifference in connections which will preferably be employed according towhether light trip or dark trip is utilized. If the apparatus isconnected for light trip operation the photoelectric tube is providedwith a negative potential source through a voltage divider consisting ofresistors 131, 132 and 133 in series connected to the negative terminalof the power supply 115 and to ground through switch contacts 134. Forthe sake of adjustment the resistor 132 is preferably provided with asliding tap 135. The photoelectric tube 98 is connected between the top135 and the control grid of the pentode 99, preferably in series withthe current limiting resistor 136. For light trip the connections aresuch that the anode 137 of the photoelectric tube 98 is connected to theamplifier input through the change-over switch blade 138. Also, forlight trip, the cathode 139 of the photoelectric tube 98 is connected tothe voltage divider tap 135 through the change-over switch blade 141 andthe resistor 136. Preferably, a smoothing condenser 142 is connectedbetween the ground terminal of the power supply 114 and the inputterminal of the photoelectric tube. The function of the change-overswitch 129 is merely to reverse the connections of the photoelectrictube 98 and to reverse the polarity of the voltage supplied theretowhere dark trip is desired instead of light trip.

Where the thyratron 101 is employed, it is preferably connected to thepositive terminal of the power supply 114 through a resistor 143 shuntedby a smoothing condenser 14. Since tubes of the thyratron type remainconductive even after removal of control voltage, an intermittentcircuit-opening switch is provided, taking the form in the arrangementillustrated of the brushes 81 and 82 cooperating with the contactsegment 86 of the drum switch 79.

In order that the falling object 36, which is to be sorted by theapparatus, will be illuminated on all sides, but only by diffused light,and the photoelectric tube 98 will be affected only by light reflectedfrom the surfaces of the falling object 36 or the reference backgrounds.97, all of the inner surfaces of the lamp housing 16 are preferablypainted with flat white lacquer, except the inner surfaces 145 of theshields 48 and 49 which are painted with flat black lacquer.

The angular position of the output tip end 146 of the helix 25 of thescrew conveyor 95 on the shaft 23, and the angular positions of the cam64, the crank disc 75 and the drum switch 79 on the timer shaft 15relative to each other as interconnected by the gears 32 and 33, thepulley 35 and the belt or chain 34, are as indicated in the schematicdiagram of Fig. 9.

The lemon or other article L being carried along the conveyor 12 reachesthe end of the conveyor above the upper gate 27 when the timer shaft 15and the drum switch 79 are in the angular position represented by 300degrees, e. g. in Fig. 9. At this instant both pairs of brushes 81, 82and 83, 84 are in contact with their respective contact segments 86 and8']. Slightly later, e. g. at 360 (6), the cam 64 reaches the angularposition in which the cam follower 63 follows along the portion "78 ofthe cam 64 causing the sectors 53 of the gate to open allowing thearticle to fall into the lamp housing 16 along the axis 183 thereof, asrepresented at 36. The article 38 remains within the field of view ofthe photoelectric tu'oe 98 (defined by the lines 158, 159 in Fig. as thetimer shaft moves from the, angular position 132 to the angular position168 degrees. During this time electrical circuit between the brushes 81and 82 remains closed by the segment 86, but the electrical circuitbetween the brushes 83 and 84 is open, as they now ride upon theinsulating portion 85 of the drum 79. Accordingly, the condenser 188 isdisconnected from the normalizer potential at the cathode of the cathodefollower 112.

If the light reflected from the lemon 36 exceeds a pre determined valuethe resistance of the photoelectric tube 98 falls to such a value as tocause the input voltage to the pentode 99 to fall below the value atwhich the potential on the negative plate of the condenser 108,connected to the brush 83, exceeds the predetermined reference voltage,e. g. volts, which causes the potential of the thyratron grid to riseabove minus four volts and to fire the thyratron 181. Thereupon, currentflows through the trip coil 72 retracting the armature 71 and allowingthe spring 68 to lower the gate 51. Accordingly, the lemon 36 falls uponthe chute 52 and slides into the light lemon receptacle 21. On the otherhand, if the lemon had been darker than the predetermined value it wouldhave fallen upon the lower gate 51 and would have been deflected intothe dark lemon receptacle 20.

During the time subsequent to the interval required for the lemon 36 tofall through the field of view of the photoelectric tube 98, the drumswitch 79 travels through the angular positions in which the brushes 83and 84 are in contact through the segment 87. The photoelectric tube 98is then illuminated only by the light reflected from the referencebackgrounds 97. The anode potential of the pentode 99 acquires a valuedetermined by the circuit constants. Since the negative plate of thecoupling condenser 108 is held at the reference voltage, e. g. 80 volts,by the connection to the cathode of the cathode follower 112 which hasits control grid biased at 80 volts, the potential difference betweenthe plates of the condenser 188 is restored, if necessary, to such avalue that when the brushes 83 and 84 are again disconnected thepotential of the negative plate of the condenser 188 will rise or fallabove or below the reference voltage, such as 80 volts, according towhether illumination of the photoelectric tube has been increased ordecreased by presence of a falling article. Therefore, the apparatus isautomatically reset or normalized after each operation so as to respondaccurately to the presence of any object having a reflective powergreater than the reflective power of the backgrounds 97, as in the lighttrip operation and vice versa in the case of dark trip operation.

If any charging current is necessary for correcting the relativepotentials on the two plates of the coupling condenser 188, it issupplied by increasing or decreasing the anode-cathode current flow inthe cathode follower tubes 189 and 112, since the current in acathode-follower automatically increases or decreases whatever amount isnecessary to cathode potential to follow control grid potential. It isunnecessary for any current to be drawn through the pentode loadresistor 102 or through the resistors 123 and 124 of the referencevoltage source. Consequently, these resistances do not enter into thetime constant of the charging circuit of the condenser 108. The timeconstant is, in effect, very small for the reason that the effectiveresistances of the cathode follower tubes 109 and 112 are relativelysmall and, furthermore, it is characteristic of cathode follower tubesthat their output impedances, determinative of time-constant effect, areproportional to the ratio of load impedance to transconductance.

normalized through the switches 83, 84 and 87 very rapidly during thetime interval permitted within an operating cycle which must be verysmall in the case of presentation of articles to be sorted .at a highrate of speed. I have found, for example, that an accuracy and stabilityexceeding 100 times that obtainable without the use of cathode followershave been obtained. The gain in stability is the product of the increasein size of coupling condenser and of the increase in rapidity ofnormalizing. Inasmuch as the value of automatic sorting depends upon thefineness of decisions which may be made in rejecting or acceptingarticles deviating but slightly from the background or standard inreflected power, any increase in sensitivity is of the utmostimportance. Reliable operation of a photoelectric sorting machine inresponse to a change of one percent in illumination of a photoelectrictube has heretofore been possible. However, I have been able to obtainresponse reliably to changes only one hundredth as great by use of thearrangement herein described, because of a hundred-fold increase instability.

The increased precision and speed obtained is of particular value incertain locations, such as in tropical countries, e.. g. where thedifficulty of maintaining insulation and overcoming. the effects ofmoisture is very great and these effects are highly deleterious owing toproducingchanges in. the effective resistances of circuit constants andintroduction; of leakage paths allowing the setting of the apparatus todrift from one operating cycle to the next, unless the arrangementdescribed herein is employed. Obtaining reliable operation entailsconsideration not only of the precision obtainable when the ap paratusis first installed and immediately after adjustment, but also the pointat which the apparatus will respondwithout resetting after a period oftime. Numerous factors tend to changethe effective setting such as agingof amplifier tubes, variation in filament voltage, imperfect socketconnections of lamps and tubes, change in cathode emission, aging ofphoto tubes, change in resistance of photo tube load resistors andchanges in other resistors, dirt or fingerprints on lens surfaces, duston lamp or housing, aging of illuminating lamps, changing candle powerand changes in lamp voltage.

In a multistage amplifier a two-volt drift in a tube results in a40-volt drift in the next tube if the gain is only twenty to one. Thus,if one hundred volts is the signal obtained by a change from white toblack of an object in the lamp housing or viewing chamber, a twovoltdrift of a tube would cause serious error. In my apparatus all thesesources of error are compensated for during each cycle between viewingof successive objects.

Although for the sake of simplicity I have illustrated an arrangement inwhich a single photoelectric tube 98 is employed in connection withmirrors 91 and 92 for viewing all sides of an object in the gravitysorter, it is to be understood that my invention is not limited thereto.For example, as illustrated in Fig. 12, if desired, three photoelectrictubes 147, 148 and 149 may be provided, which are mounted at the sidewalls of the lamp housing 16 alternate with the positions of thebackgrounds 97. In this case separate amplifiers 151, 152 and 153 areprovided for each photoelectric tube, arranged for tripping parallelconnected thyratrons 154, 155 and 156. The arrangement is such that ifany one of the photoelectric tubes 147, 148 and 149 is illuminated inexcess of the standard value (or less in the case of dark trip) one orthe other of the thyratrons 154, 155 and 156 is ignited and current iscaused to flow through the tripping coil 72 as in the arrangement ofFig. 13. Once during each operating cycle the anode circuits to all ofthe thyratrons 154, 155 and 156 are broken by the insulating portion ofthe drum 79 between the brushes 81 and 82.

The hexagonal lamp housing 16, or housing with optical elements spacedat 60 degrees or multiples thereof, has

the advantage of a high degree of versality as it may be employed, asshown in Figs. 12 and 13, for obtaining illumination on all sides of anobject in the gravity sorter integration of reflectivity ofsubstantially the entire surface or photoelectric response to all sidesthereof. In addition, it may be used. in connection with point-bypointor' two-dimensional scanning, such as described in my copendingapplication Serial No. 3,876, filed January 23, 1948, now Patent2,474,230, granted June 28, 1949. It may, if desired, also be employedin cases where it is desired or necessary to observe only one side ofthe object, in which case only one of the photoelectric tubes 147, .148and 149 and one corresponding amplifier and tripping mechanism need beemployed.

While the invention has been described as embodied in concrete form andas operating in a specific manner in accordance with the provisions ofthe patent statutes, it should be understood that the invention is notlimited thereto, since various modifications will suggest themselves tothose skilled in the art without departing from the spirit of theinvention, the scope of which is set forth in the annexed claims.

What I claim is:

l. A normalizer circuit for a photoelectric sorter circuit having aphotoelectric tube followed by a plurality of electronic tubes, the lasttube having a control electrode, the preceding tube being connected as acathode follower and having a cathode with a condenser coupling saidcathode to said control electrode, said normalizer circuit comprising incombination with such a cathode follower and condenser a fixed-potentialterminal and an intermittently closing switch between said controlelectrode and said fixed-potential terminal for adjusting the charge onsaid condenserto restore the control-electrode potential to that ofthefixed-potential terminal without introducing large timeconstant effectsduring the closure of theswitch.

2. A normalizer circuit for a photoelectric sorter circuit having aphotoelectric tube followed by a plurality of stages of electronicamplifiers, the last stage comprising a tube having a first controlelectrode, the preceding stage comprising a cathode follower tube havinga first cathode with a condenser of large capacity coupling said cathodeto said control electrode, said normalizer circuit comprising a secondcathode follower having a second control electrode and a second cathode,an intermittently closing switch between said first control electrodeand said second cathode, and a source of fixed-potential connected tosaid second control electrode.

3. A fast normalized amplifier circuit for a photoelectric sortercomprising in combination, a pentode tube having an anode and a largeanode resistor to produce maximum gain, a cathode follower tube, havinga first control electrode connected to said anode and having a firstcathode, a following stage comprising a tube having a second controlelectrode, a condenser of relatively large capacity connected betweensaid first cathode and said second control electrode, a source ofpredetermined potential, and an intermittently closing switch betweensaid source and said second control electrode for adjusting the chargeon said condenser rapidly to such a value as to restore a predeterminedbias potential to said following stage independently of variations incircuit conditions while assuring retention of such bias by saidfollowing stage during the entire interval between successive closuresof said normalizer switch for providing sensitivity and precision ofresponse of said following stage.

4. A fast normalized amplifier circuit for a photoelectric sortercomprising in combination, a pentode tube having an anode and having alarge anode resistor to produce maximum gain, a cathode follower tube,having a first control electrode connected to said anode and having afirst cathode, a following stage comprising a tube having a secondcontrol electrode, a condenser of 15 relatively large capacity connectedbetween said first cathode and said second control electrode, a sourceof predetermined potential, a second cathode follower having a secondcathode and having a control electrode connected to said potentialsource, and an intermittently closing normalizer switch between saidsecond cathode and said second control electrode for adjusting thecharge on said condenser rapidly to such a value as to restore apredetermined bias potential to said following stage independently ofvariations in circuit conditions while assuring retention of such biasby said following stage during the entire interval between successiveclosures of said normalizer switch for providing sensitivity andprecision of response of said following stage.

5. A fast normalized circuit for a photoelectric sorter comprising incombination a tube having a loaded anode, a cathode follower tube havinga first control electrode connected to said anode and having a cathode,a tube having a second control electrode, a condenser between saidcathode and said second control electrode, a source of predeterminedpotential, and a switch between said second control electrode and saidpotential source for adjusting the charge on said condenser rapidly tosuch a value as to restore a predetermined bias potential to saidfollowing stage independently of variations in circuit conditions whileassuring retention of such bias by said following stage during theentire interval between successive closures of said normalizer switchfor providing precision and sensitivity of response of said followingstage.

6. A fast normalized circuit for 'a photoelectric sorter comprising incombination a tube having a loaded anode, a cathode follower tube havinga control electrode connected to said anode and having a cathode, a tubehaving a second control electrode, a condenser between said control andsaid second cathode electrode, a source of predetermined potential, asecond cathode follower having a second cathode and having a controlelectrode connected to said potential source, and a switch between saidsecond control electrode and said second cathode for adjusting thecharge on said condenser rapidly to such a value as to restore apredetermined bias potential to said following stage independently ofvariations in circuit conditions while assuring retention of such biasby said following stage during the entire interval between successiveclosures of said normalizer switch for providing precision andsensitivity of response of said following stage.

7.. A normalizer circuit for a photoelectric sorter circuit having aphotoelectric tube followed by a plurality of electronic tubes includinga high gain amplifier tube with a large anode resistor for high gain,the last tube of such a plurality having a control electrode, saidnormalizer circuit comprising a tube being connected as a cathodefollower and having a cathode, a condenser having a capacity of theorder of tWo microfarads for maintaining its potential differencesubstantially independent of insulation resistance in the circuits,coupling said cathode to said control electrode, a fixed potentialterminal and an intermittently closing switch between said controlelectrode and said fixed potential terminal for intermittently adjustingthe charge on said condenser to restore the control electrode potentialto that of the fixed potential terminal without introducing largetime-constant effects during closure of the switch while retaining thelong time constant of such condenser with insulation resistance forcoupling said last tube while said switch is open.

References Cited in the file of this patent UNITED STATES PATENTS2,055,748 Lubcke Sept. 29, 1936 2,095,124 Cockrell Oct. 5, 19372,139,489 Cockrell Dec. 6, 1938 2,525,020 De Jarlais Oct. 10, 1950

